Dieter Krombach has been sentenced to 15 years in prison over the death of his stepdaughter almost 30 years ago. Photograph: AFP/Getty Images

A French court has convicted a German doctor of unintentionally killing his stepdaughter almost 30 years ago.

Dieter Krombach was sentenced to 15 years in prison for drugging 14-year-old Kalinka Bamberski and causing her to die of suffocation at his home near Lake Constance, in Germany, in 1982.

The verdict was the end of a three-decade attempt by the girl's father, André Bamberski, to bring the 76-year-old cardiologist to justice. Bamberski is facing charges for allegedly kidnapping Krombach from his home after the German authorities refused to extradite him.

Krombach was found tied up and bleeding outside the prosecutor's office in Mulhouse, near the German border, two years ago. Bamberski, 73, a retired accountant, has said he approved of the kidnapping of Krombach but denied taking part in it.

Kalinka and her brother were staying with their mother when she was found dead in her bed in July 1982. Krombach admitted giving the girl an iron injection, reportedly to help her improve her suntan, but denied killing her.

A German court ruled the death accidental, but a French court found Krombach guilty in his absence in 1995. The European court of human rights ruled the cardiologist had been denied a fair hearing and the right to an appeal.

On Saturday, the Paris court convicted him of "deliberate violence leading to involuntary death".

In a final plea, Krombach said: "I never hurt Kalinka." His lawyer announced that he would appeal against the "unreasonable" verdict.

Bamberski welcomed the judgement, saying: "Of course my first thought is for Kalinka. What I promised her, what I wanted was a complete and fair trial. Now that goal has been reached.

"Justice has been done in her memory, and now I will be able to mourn for her."